One-dimensional pore structures are produced through extrusion. The product is usually called the honeycomb structures under the category of cellular structures.
Two-dimensional pore structures are also produced for heat transfer applications though various methods.
The three-dimensional structures are made through three dominant methods. These are foaming, foam replication, and solid free forming or 3D printing processes.
The foaming or replication process is limited to producing non-uniform pore structures. The geometry of the pores is dictated by the formation, growth, and impingement of gaseous cells. In general, pores are spherical in shape. In addition, the openings are not uniform and the variation in pore size could be an order of magnitude.
The 3D printing process or solid free forming produces three-dimensional porous structures by depositing materials using one or several nozzles at once. This process builds the desired structure layer by layer; it is time consuming, limited to few materials, and costly.